Circadian Rhythm

What is Circadian Rhythm?

Also known as your sleep/wake cycle, your circadian rhythm is basically your 24 hour biological variations controlled by your body’s biological clock.  This 24-hour internal clock is running in the background of your brain and cycles between sleepiness and alertness at regular intervals.

For most adults, the biggest dip in energy occurs at the middle of the night when fast and just after lunchtime when craving a post-lunch nap. Those times can be different if you’re naturally a night owl or a morning person.  At the same time, your circadian rhythm is stable if you have enough sleep.

What affects circadian rhythm?

This is one of the several body rhythms modulated by your hypothalamus including regulation of body temperature, hormone secretion and immune response.

The circadian biological clock is controlled by a part of the brain called the Suprachiasmatic Nucleus (SCN), a group of cells in the hypothalamus that respond to light and dark signals. From the optic nerve of the eye, light travels to the SCN, signaling the internal clock that it is time to be awake. The SCN signals to other parts of the brain that control hormones, body temperature and other functions that play a role in making us feel sleepy or awake. Therefore, when it’s dark at night, your eyes send a signal to the hypothalamus that it’s time to feel tired. Your brain, in turn, sends a signal to your body to release melatonin, which makes your body tired.

Sleep disruption happens when your circadian rhythm and light are in conflict and does not coincide with the cycle of daytime and nighttime. This is usually observed among travels having jet lag at different time zones or shift workers having difficulty sleeping during the day and staying awake at night.

When does circadian rhythm work best?

Your circadian rhythm will likely change as you get older or you may not have the same rhythm as your partner, child or parents. Your circadian rhythm works best when you have regular sleep habits. This is when you go to bed at night and wake up in the morning around the same times on a daily basis including weekends.

Meanwhile, when your regular sleep habits are disrupted like during daylight savings time or staying late watching your favorite movie or TV show, you may feel out of sorts and can make it harder to pay attention. During these times, all you have to do is catch up and get enough sleep the following day.

The diagram below demonstrates the circadian alerting signal. You will definitely feel better when you pay more attention to your body and notice feelings of alertness and drowsiness at different times of the day. Hence, you also need to spend more time developing good sleep hygiene habits.

Sources:

• Henry G. Raroque, MD. (2014). Lecture notes on Introduction to Sleep. The Dallas School of Neuroscience and Sleep Medicine, Texas.
• Sleep.org by National Sleep Foundation, Maryland.  What is Circadian Rhythm?. Retrieved on March 2018 at  https://sleepfoundation.org/sleep-topics/what-circadian-rhythm.